Transmission network



March 27, 1934. Q Q ET AL 1,952,411

TRANSMI S S ION NETWORK Filed March 16, 1928 2 Sheets-Sheet l INVENTORSOTTO BORN BY WI LM SER ATT N EY March 27, 1934. o, BQHM Er AL 1,952,411

TRANSMI S S ION NETWORK Filed March 16, 1928 2 Sheets-Sheet 2 24 jig. 2c

Patented Mar. 27, 1934 PATEil IFFICE 1,952,411 TRANSMISSION NETWORK OttoBiihm and Wilhelm Moser, Berlin, Germany,

assigncrs to Telefunken Gesellschaft fur Drahtlose Telegraphic m. b. H,Berlin, Germany, a corporation of Germany Application March 16, 1928,Serial No. 262,160 In Germany March 17, 1927 4 Claims.

It has been found in practice that in the case of short-wave work it issuitable to radiate the energy from a plurality of wires arranged acertain distance apart rather than from a single 5 antenna wire, itbeing immaterial so far as thepresent invention is concerned in Whatparticular way these aerials are geometrically disposed.

However, all systems comprising a plurality of aerials have this featurein common that the constituent antennzeare equivalent with reference toone another, and that they must be identically coupled with thetransmitter. The coupling is effected by means ,of energy. (feeder)wires, and these, of course, must be branched whenseveral antennae areemployed.

In order that the energy of the transmitter may be totally transmittedto the different aerials, it isunecessary that the energy lines shouldbe coupledwith one another and with the respective antennae in a wayfree from reflection. The same situation holds true if av receiver is tobe coupled with a plurality of aerials. In other words, at eachbranchingpoint of the energy line, say, atrthe junction or transitionpoint from 1 to 11. wires, the natural impedance of all of these nwiresmust be equal to that of. the main line, in other words, eachindividual line must possess the 'n-fold resistance of the main line. Ifeach of these in many lines again divides into a number of others, thesame condition holds true for such new branch point. Finally, however,also the useful, thatis, the antenna resistance'must be adapted to theenergy line.

It has already been known from low-frequency -problems, ,f0r instance,from ordinary telephone lines that the natural impedance of the mainenergy'line maybe adapted to that of the branch nes by the aid oftransformers having conveniently chosen transformation ratios. But theqi qu stion of dimensioning and disposing the lines was mainly solvedfrom a viewpoint of insuring minimum cost of installation, indeed,suchlack in agreement between the wave resistance as resulted from suchpolicy and plan was corrected iby the convenient selection of thetransformation ratios of coupling transformers.

Now, in the case of radio frequency work, especially with ultra-shortwaves, transformers, most preferably of the air-core type, could beemployed 'ifor the said purpose. However, these involve the disadvantagethat they establish coupling not in a purely inductive manner, but alsocapacitively, so that as a consequence the phase relations between theprimary and the secondary bibecome uncertain. When the question ofproper phase relationship is important (and this is the case oftransmitting and receiving with a great number of antenna which are tobear well-defined phase relations with one another by being arranged atcertain distances), it is a better plan 5 not to use such uncertaintransformer coupling and to couple the energy lines at thejunctionpoints directly with one another. v According to thedisclosuresof the present invention, while dispensing with the said couplingtransformers by establishingdirect connection between the input andoutput wires at the junction points, wave reflection is completelyprecluded by that the necessary conditions and relations as regardsnatural impedance are insured 7 simply bythe convenient selection of theline constants for themain and branch lines. The factors governing theline or wire constants are the cross-sections and the geometrical formof arrangement of the wire paths, the distances ductors, becomes higherwhenever the geometrical size of the line path, for instance, in thecase of wires, the cross-section is increased. Hence, by enlargingthecross-section, the natural impedance can be diminished. A reduction inthe distance between conductors, or an increase in the dielectricconstant of the medium surrounding the line, would have the same effect.9

For the supply of antennae according to the present invention, thefollowing forms of line paths may be considered:

(a) Concentric tubes whose diameters are changed at each branch point inaccordance with whatever change in natural impedance may be desired.

(b) Parallel wires or tubes whose mutual distanceor whose cross-sectionsare varied at each branching point.

(0) Parallel wires or tubes which are screened towards the outside by acommon sheath or envelope. In this case, there is a further chance toutilize the influence of the envelope upon the line capacity forinsuring the desired natural 119 Ra=120 ohms.

diameter). have a natural impedance each of Z3=120 ohms,

impedance, for instance, by varying the distance between the envelopeand the lines.

(11) Lines consisting of several paths, parallel from both an electricalas well as spatial viewpoint with or without external screening orshielding by external envelopes. In this case, there is an additionalchance to vary the natural impedance at the branching points by that thenumber of paralleled conductors may be altered.

All of the arrangements hereinbefore mentioned may be embedded ininsulation materials possessing well defined dielectric constants, thevalue of the dielectric constant being taken into consideration inchoosing the dimensions of the diiierent conductor parts.

As regards the last conductor section directly preceding the antenna,its natural impedance must suitably be so chosen that it will come asclosely as possible to the antenna resistance. The coupling between theenergy line and the antenna isthen to be chosen of the simplest possibleform.

The following practical example furnishes numerical values for an energyline to be dimensioned according to the present invention and as shownin the accompanying drawings.

The problem to be solved is to establish coupling between a transmitterS and four identical antennae A, the latter to be excited at the samephase. Suppose the resistance of each aerial is Each antenna is to becoupled with the respective energy supply line directly without theinsertion of a transformer.

According to the present invention, this is e1- fected by that thetransmitter first works upon a main supply line having a naturalimpedance Z 1=30 ohms. This main line may consist of two concentrictubes, the outer tube having a diameter of 100 mm. and the inner tube adiameter of 60 mm. This main line is divided or branched into mm. Thesaid two secondary lines are again branched each into two energy lines(consisting again, for instance, of concentric tubes, the outer one of100 mm. and the inner conductor of 12.5 These last-named conductors sothat they can be coupled directly with the antenna in a way afiordingfreedom from refiection.

Having thus described our invention what we a plurality of pairs ofspaced aerials, a transmission line of known impedance coupled to highfrequency apparatus, said transmission line comprising concentricconductors of known mutual capacity, direct connections between eachantenna in each pair and an antenna in another pair, and a plurality ofbranch lines directly included in said connections and directlyconnecting said connections to the transmission line, said branch linescomprising concentric conductors of less mutual capacity than saidtransmission line and each having an overall impedance greater than theimpedance of the transmission line.

2. An antenna system having, in combination, a plurality of pairs ofspaced aerials, a transmission line of known impedance coupled to highfrequency apparatus, direct connections extending between each antennain each pair and an antenna in another pair, said direct connectionsincluding a plurality of branch lines directly connected to thetransmission line, said branch lines each having an overall impedancegreater than the impedance of the transmission line, said transmissionline and branch lines comprising spaced conductors, the spacing betweenthe branch line conductors being greater than the' including tubeshaving diameters different from said branch lines.

4. An antenna system having, in combination, a two wire transmissionline connected to high frequency apparatus, two: pairs of antenna,idividual ground connections at each of said antenna of said pairs, adirect connection between an an-' tenna in each pair to the ground ofthe other antenna in the same pair, and a plurality of branch linesdirectly connected to said antenna connections and to said two wiretransmission line, said branch lines taken alone each having an overallimpedance greater than the impedance of said transmission line, but lessthan the overall impedance of said antenna connections taken alone.

o'rro BoHM. WILHELM MOSER.

